Sensitization of latex foam rubber to gelation



United States Patent O US. Cl. 260-25 8 Claims ABSTRACT OF THE DISCLOSURE The sensitivity of a foamed latex compound to gelation is increased by including in the foamed latex a polyalkylene polyamine obtained by condensing to a viscosity average molecular weight of 500l00,000 ammonia or a low molecular weight polyalkylene polyamine such as tetraethylene pentamine with an aliphatic hydrocarbon containing two groups reactive with amines and at least one of which groups is a halogen atom, such as dichloroethane.

This invention relates to the preparation of latex foam rubbers and more particularly to the step of gelling the foamed latex during the preparation procedure.

In preparing latex foam rubbers, a high solids content latex normally containing higher than 55% and usually higher than 60 weight percent total solids is compounded with the required materials, foamed, moulded, gelled, vulcanized, washed and dried. Compounding materials may include foaming agents, fillers, antioxidants, vulcanizing agents, vulcanization accelerators, gel sensitizers, gelling agents, etc. In order that foam rubbers having acceptable physical properties and appearance may be obtained, it is necessary to have the gelation take place before breakdown of the foam structure begins. To speed up or sharpen up the gelling action, it is normal practice to include a secondary gelling agent commonly called a sensitizer or gell sensitizer among the materials compounded into the latex. When moulded latex foam rubbers are produced by the Dunlop process, the two most widely used gelling agents are sodium silicofluoride and ammonium acetate and the most popular gel sensitizer is a reaction product of ethyl chloride, formaldehyde and ammonia, most often identified by the trademark Trimene Base. Guanidines such as diphenyl guanidine, low molecular weight polyamines such as triethylene tetramine and tetraethylene pentamine, cationic soaps and certain phenols and water-soluble silicates also have been employed as gel sensitizers. While all of the abovementioned gel sensitizers are varyingly effective, improvements are desirable with respect to their individual effect on one or more considerations such as colour imparted to the foam rubber, amount of sensitizer required to be used, foamability of the latex, foam fluidity, foam stability, toxicity, cost and availability of the sensitizer compound.

It has now been found that polyalkylene polyamines characterized by a viscosity average molecular weight of about 500-100,000 can be used as gelation sensitizers to prepare latex foam rubbers of improved whiteness and lower cost.

More specifically, it has been found that improved latex foam rubbers may be produced in a process comprising compounding, foaming, gelling and vulcanizing a latex of a rubbery polymer containing at least about 55 weight percent solids, by the step of including in the foamed latex prior to gelation of the foam a condensation product of a nitrogen-containing compound described by the 3,493,523 Patented Feb. 3, 1970 ICC general formula H(HNC H NH where n is 1-3 and x is 0-6, with a C -C aliphatic hydrocarbon compound having at least two separated reactive groups which are reactive with amines, at least one of which is a halogen atom, the condensation product being characterized by a viscosity average molecular weight in the range of about 500100,000 and being employed in amount of 0.1l.0 part by weight per parts by weight of total solids in the uncompounded latex, said nitrogen-containing compound and said halogen-containing compound being reacted in a molar ratio of 0.5-3.5/1. respectively.

The two basic gelling systems for latex foam rubber are (1) heat gelling in which the application of heat causes phase inversion of a foam and (2) delayed-action gelling systems in which phase inversion takes place in a controllable predetermined time without any substantial change in temperature after the addition of the gelling agent. The high molecular weight polyalkylene polyamines of the present invention may be used to sensitize the latex foam in each system but application is particularly visualized in the delayed-action systems in which acid-acting fluo complexes such as sodium silicofluoride, whether in combination or not with a compound functioning such as zinc oxide does, are most often employed as the gelling agents.

The high molecular weight polyalkylene polyamines may be described as comprising condensation products of nitrogen-containing compounds described by the general formula H(HNC,,H NH where n is an integer, preferably l3 and x is zero or more and preferably 0-6, with lower aliphatic hydrocarbon compounds, i.e., C -C having at least two separated reactive groups reactive with amines at least one of which groups is a halogen atom. Examples of suitable groups which are reactive with amines are epoxy, hydrogen sulfate, chlorine, bromine, etc. radicals. The preferred lower aliphatic compounds contain 2-3 carbon atoms and chlorine or bromine as the halogen. As examples of suitable nitrogen-containing compounds, there may be mentioned ammonia, ethylene diamine, propylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, dipropylene triamine, tributylene tetramine, etc. The halogen-containing lower aliphatic compounds may be exemplified by compounds such as 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,2-dibromoethane, 1,3-dibromopropane and other haloalkanes preferably containing a halogen atom on each terminal carbon atom, epichlorohydrin, epibromohydrin, alphadichlorohydrin, etc. It has been found that the condensation products may be employed in solution in water or alcohol and they may be in free base or hydrohalide form. Effective products are obtained when about 0.5-3.5 moles of the nitrogen-containing compound are reacted per mole of the halogen-containing compound with the preferred ratio being 1-3/l. A particularly suitable product is obtained by condensing ammonia with 1,2-dichloroethane at about a mole for mole ratio to a molecular weight of about 500-1500 so as to contain a minimum amount of tertiary nitrogen and isolating the product in the free base form.

The gelation sensitizing agents may be applied to the production of latex foam rubbers from high solids content latexes of rubbery polymers which may, if desired, be blended with minor proportions of latexes of resinous polymers. As examples of rubbery polymers, there may be mentioned homopolymers of low molecular weight conjugated diolefins such as butadiene-1,3, isoprene, chloroprene and piperylenewith natural rubber being considered as a homopolymer of isoprene, and copolymers of these conjugated diolefins with each other or with one or more copolymerizable monoolefinic monomers such as styrene, acrylonitrile, acrylic acid, methyl methacrylate,

3 4 vinyl chloride, vinyl acetate, etc., while as resinous polyagent and the sensitizing agent should preferably be added mers there may be mentioned polystyrene, po1yacryl0- as a solution in water. The best solution concentration is nitrile, polyvinylidene chloride, polyvinylchloride, polyvariable depending on the particular sensitizer used. The vinylacetate, polymethylacrylate and copolymers of the presence of formaldehyde in the sensitizer is undesirable monomers of the foregoing resinous polymers, etc. Included also would be copolymers of the foregoing monoas it has been found to raise the viscosity and coagulum level undesirably in the compounded latex. The comolefinic monomers with minor proportions of diolefinic pounding ingredients are normally incorporated into the monomers and graft copolyrners of one or more of the latex and foam at ambient temperatures as is the gelling foregoing monomers with one or more of the foregoing agent. As indicated earlier, acid-acting alkali metal silicopolymers. fluorides are most often employed as the gelling agents In preparing the latex foam rubbers, the usual comand they are usually employed in combination with zinc pounding ingredients and procedures can be employed. oxide. Other acid-acting gelling agents such as ammonium Generally, the compounding is carried out in two stages. acetate and ammonium sulphate may be used also, Nor- In the first stage, the vulcanizing agent and one or more mally 0.5-5 parts by weight of each of zinc oxide and the vulcanization accelerators are blended into the latex. acid-acting gelling agent are employed, and in the present There may also be added at this stage other frequently invention the preferred level appears to be about 2-3 used materials eg a process oil, an antioxidant, a soap, a parts. filler water and the gelation sensitizing agent and the The following examples illustrate the invention and compounded latex is allowed to mature if desired. The certain of its specific aspects more thoroughly. All parts latex is next foamed by beating air into it by mechanical are by dry weight. agitation and after the foam volume has been raised to EXAMPLE I the desired extent, the gelling agent is thoroughly blended, i.e. compounded into the foam. The foamed latex is then poured into moulds and permitted to gel to reticulation either at ambient temperatures or after warming to about -45 C. The gel is then vulcanized by raising the temperature to the desired level e.g. about 100 C.

The above-mentioned compounds may be incorporated into the latex in the quantities usually employed. Thus the compounded latex may contain for every 100 parts by 30 weight of vulcanizable rubbery polymer 1-5 parts by weight by vulcanizing agent which is usually sulfur, 0.5- 7.5 parts by weight of vulcanization accelerator e.g. zinc diethyl dithiocarbamate and zinc Z-mercaptobenzothiazole, l-50 parts process oil, 0.5-2.0 parts antioxidant e.g. 2,2'-methylene-bis(4-methyl 6 tertiary butyl phenol), 0.1-5 parts of soap e.g. caster and tall oil soaps, potassium, oleate etc., O-200 or more parts of filler e.g. clay, whiting, talc, lithopone, etc., water when desired to reduce the total solids level, and gelation sensitizer. The amount 4 of the gelation sensitizer of the present invention to be used is variable depending on the particular compound chosen and may vary generally from about 0.1 to 1.0 part dry weight i.e. 100% activity basis, per 100 parts by weight of total solids in the uncompounded latex. It is preferably between about 0.2 and 0.6 part with latexes comprising rubbery butadiene-styrene copolymer when the hydrochloride form of the condensation product of 1,2-dichloroethane and ammonia is used. When this condensation product is in the free base form, the preferred amount A synthetic latex having a total solids content of about 65 weight percent with about 15% of the polymer particles in the latex being polystyrene and about 85% of the polymer particles being a rubbery copolymer of butadiene and styrene containing about 22% copolymerized styrene was compounded both by itself and mixed with deammoniated natural rubber latex in the recipes shown in Table I using two gelation sensitizing agents of the present invention. sensitizer A, which was used as a 4.5% solution in water, is the condensation product obtained by reacting 1,2-dichloroethane and ammonia in a molar ratio of 1/2.5. It had a molecular weight in the range of about 500-1500, contained about 25 Weight percent each of primary and secondary amino groups and about 50% tertiary amino groups mostly as piperazine rings and was recovered in hydrochloride form. Sensitizer B, which was used as a 7.5% solution in Water, was obtained by condensing the same reactants in a molar ratio of 1/1 to a molecular weight of about 500-1500. It was recovered in the free base form and contained 50-70% tertiary amino groups in predominantly non-heterocyclic form. Triethyl trimethylene triamine was used as a comparison sensitizer as a solution in waterit being a widely used sensitizer more popularly known by its trademark Trimene Base.

The latex compounds were matured overnight at room temperature in a 50% humidity atmosphere prior to addi- 50 tion of the zinc oxide, foaming and addition of the gelling agents. Foaming was done in a Hobart mixer. Curing was is bfitweell about and 035 p It h began found f carried out for 25 minutes in live steam for all samples Vantageous Whfin 115mg the hydl'ochlofldfi form to 1156 except 9 and 10 which were cured for 18 minutes at 325 the pH of the compound to 10.5-11.5 with a fixed al i F. in a force-air circulating oven. The latex foam rubbers such as potassium hydroxide before adding the sensitizing were tested as shown in Table I.

TABLE I Sample No 1 2 3 4 5 6 7 8 9 10 11 12 13 Synthetic latex solids 1 Natural latex 50 Zinc diethyldithiocarbamate. 1.0 1 O 1 0 1 0 1.0 1. 0 1.0 1. 0 1. 5 Zinc mercaptobenzothiazole" 1. 0 1 O 1. 0 1 0 1. 0 1. 0 1. 0 1. 0 1. 0 Sulphur 2.0 2 O 2.0 2 0 2.0 2.0 2. 0 2.0 2. 5 Antioxidant..."- 1.0 1 0 1.0 1 0 1. 0 1. 0 1.0 1. 0 1.0 Potassium oleate 0 4 0 4 0. 4 0. 4 0 5 Castor oil soap."

Potassium hydroxide.

Ammonia Feldspar sensitizer A (pure basis) sensitizer B (pure basis). Trimene Base (as received Sodium silicofluoride Ammonium acetate Zinc oxide Compound properties:

Viscosity, poise 4. 0 10. 5 Coagulum, percent. 0. 01 C 3 pH 10. 7 10.8 Processing:

Froth time, minutes 1. 7 2. 25 From viscosity, poise. 43 43 Gel time, minutes 7. 13. O

TABLE L-Oontinued Sample No 1 2 3 4 5 6 7 8 0 10 11 12 13 Gel pH Gel range, parts ammonium acetate Foam structure Physical properties:

Density, lbs/ft. Compression set, percentm. Elongation at break, percent Teusile strength, lbs/in. Compression modulus at 25% compression, lbs./in.

40% compression, lbs/in). 80 50% compression, lbs/111. 66 Permanent set, percent 6 2 .0 Modulus loss after flexing at 25% compression, percent 8. 9 13. 3 40% compression, percent.-. 7. 1 8. 7 50% compression, perceut 0 0 0.0 Flex set, percent 3 0 2.6

These results show that excellent quality foam rubbers and styrene containing 22% copolymerized styrene, can be prepared with the novel sensitizers of this invenwith the latex having a total solids content of 67 Weight tion and they have the advantage of being whiter in percent. colour than those prepared with the comparison sen- Latex Ca latex of a rubbery copolymer of butadiene sitizer. and acrylonitrile containing 20% copolymerized acryl- EXAMPLE II onitrile, with the latex having a total solids content of 64 weight percent.

Latex Dan artificial latex prepared from a solution of a rubbery isoprene homopolymer which had been polymerized in solution to a high cisconfiguration in its molecular structure. The latex had a solids content of 65 weight percent.

Samples of the latex of Example I were compounded 25 as shown in Table II. Maturing was at ambient temperature overnight with the zinc oxide being added shortly before foaming and the sodium silicofluoride being blended into the compounds during foaming. The compounds were run continuously through an 8 M Oakes mixer for one hour at a rate of about 235 wet pounds of The compounding recipes and results are recorded in foam per hour. At the conclusion of each run the Oakes Table III. The procedure in this series varied from that mixer was examined and found to contain little or no of Examples I and II in that the zinc oxide was added coagulum. during foaming.

TABLE III Latex A Latex B Latex C Latex D Latex solids 100 100 100 100 100 100 100 100 Zinc diethyldithiocarbamate 1. 0 1. 0 1. 0 1. 0 1. 0 1. 0 1. 0 1. O Zinc mercaptobenzothiazole 1. 0 1. O 1. 0 1. 0 1. 0 1. 0 1. 0 1. 0 Sulphur 2. 0 2. 2. 0 2. 0 2. 0 2. o 2.0 2. 0 Antioxidant 1. 0 1. 1. 0 1. 0 1. o 1 1. o 1. 0 Castor oil soap 5 0.5 0.5 0.5 0.5 Potassium hydroxide 5 0. 3 Sensitizer A 5 Sensitizer B Zinc oxide 3.0 3. 0 Sodium silicofiuoride 2. 2. 0 2. 0 Compound pH 9. 8 10. 6 10.6 Compound viscosity, poise 2.0 47 25 Froth time, minutes. 1. 2.2 2.3 1.0 Froth viscosity, poise 37 84 29 Gelation pH 8. 7 8. 3 Gelation time, minutes 8. 5 10 6. 8 Foam structure Good Good Goo Goo Good Fair Fair The results show that the use of these sensitizers will These results show that the sensitizers of this invennot cause fouling of the foaming equipment due to untion can be successfully applied to the preparation of desirable destabilization of the compounded latex. good foam rubbers from a wide variety of latexes.

TABLE II EXAMPLE IV Synthetic latex solids The latex of Example I was employed to test the effec- Zinc diethyldithiocarbamate. 1 0 Zinc mercaptobenzothiazole 1.0 tiveness of a number of other sensitizing agents described Sulphur 2. 0 below AntioxidanL g Castor oil soap.

Potassium hydrbmd Sensitizer CMethyl quaternary form of Sensitizer B.

- opt mal-rs wb o coo Sensitizer A 0 35 Sensitizer DFree base form of Sensitizer A. g gg g g li f3 Sensitizer ESensitizer A as a solution in ethyl alcohol. Sodium silicofiuoride 2.5 2.3 Sensitizer FSensitizer A with unreacted ammonia removed. EXAMPLE III Sensitizer G-Condensation product of epichlorohydrin The effectiveness of sensitizers A and B of Example I 7 with tetraethylene pentamine reacted in a molar ratio of about 1.6/1 and recovered in free base form. Mowas determined when applied to the following latexes. lecular Weight range of the product was about 500 Latex Aa high solids natural rubber latex which had 50,000,

been deammoniated to 0.2% ammonia. Sensitizer I-I-Similar to Sensitizer G but having a some- Latex B-a latex of a rubbery copolymer of butadiene what higher molecular weight range.

Sensitizer ]Similar to Sensitizer H but in hydrochloride form.

The compounding, foaming, gelling and vulcanizing procedure of Example I was followed with the recipes and results being recorded in Table IV.

TABLE IV Sensitizer C D E F G H J Latex solids 100 100 100 100 100 100 100 Zinc diethyldithiocarbamate 1. 1. 0 1. 0 1. 0 1. 0 1. 0 1. O Zinc mercaptobenzothiazole 1. 0 1. 0 1. 0 l. 0 1. 0 1. 0 1. 0 Sulphur 2. 0 2.0 2.0 2.0 2.0 2.0 2. 0 Antioxidant. 1. 0 1.0 1. 0 1.0 l. 0 1.0 1. 0 Potassium oleat 0. 4 0. 4 O. 4 0. 4 0. 4 O. 4 0. 4 Amount of sensitizen. 0. 29 0. 28 0.32 0. 0. 15 0.15 0.32 Zine oxide 3. 0 3.0 3. 0 3. 0 3.0 3.0 3. 0 Sodium silicofiuoride 2. 2. 25 2. 25 2. 25 2. 25 2. 25 2. 25 Potassium hydroxide l). 0. 31 0. 31 Compound viscosity, poise 2. 8 4. 1 4. 1 68 51 27 2 Compound pH 9. 7 11.4 11. 1 10. 4 10. 2 10. 1 11. 2 Froth time, minutes 5 2. 8 2. 0 2.5 2. 7 2. 5 3. 5 Froth viscosity, poise 67 63 48 6O 66 65 55 Gel time, minutes 7. 5 13. 5 17. 5 7. 5 8. 0 7. 0 9. 2 Gelp 8.8 8.5 8.5 8.4 8.3 8.5 8.8 Foam structure Good Good Good Good Good Good Good We claim:

1. In a process comprising compounding, foaming, gelling and vulcanizing a latex of a rubbery polymer containing at least about 55 weight percent solids, the improvement which comprises the step of including in the foamed latex prior to the gelation step 0.1 to 1.0 part by weight per 100 parts by weight of total solids in the uncompounded latex, of a condensation product of a nitrogen-containing compound of the formula where n is an integer of from 1 to 3 and x is from 0 to 6, with a C to C aliphatic hydrocarbon compound having at least two separated reactive groups which are reactive with amines, at least one of said reactive groups being a halogen atom, the condensation product having a viscosity average molecular weight in the range of about 500 to 100,000 the nitrogen-containing compound and the aliphatic compound being reacted in a molar ratio of 0.5 to 3.5 :1 respectively.

2. The process of claim 1 wherein the condensation product is in its free base or hydrochloride form.

3. The process of claim 1 wherein the condensation product is the free base form of the product obtained -by condensing ammonia with 1,2-dich1oroethane at about 1:1 molar ratio and the amount of condensation product is about 0.25 to 0.35 part.

4. The process of claim 1 wherein the condensation product is the hydrochloride form of the product 0b in the latex before the condensation product is added.

6. The process of claim 2 wherein the rubbery polymer comprises a ploymerized low molecular weight conjugated diolefinic monomer.

7. The process of claim 2 wherein the latex comprises a major proportion of rubbery polymer and in relation thereto a minor proportion of resinous polymer.

8. The process of claim 2 wherein the latex comprises a rubbery polymer selected from the group consisting of natural rubber, butadiene-styrene copolymers, butadieneacrylonitrile copolymers, polymerized low molecular weight conjugated diolefinic monomers, and blends of a rubbery butadiene-styrene copolymer with a minor proportion of a resinous styrene polymer.

References Cited UNITED STATES PATENTS 2,776,330 1/1957 Jones et al. 3,015,641 2/1962 Bawn et al. 3,015,642 2/1962 Bawn et al. 3,107,224 10/ 1963 Rodgers et al. 3,238,172 3/ 1966 Talalay et al.

SAMUEL H. BLECH, Primary Examiner MORTON FOELAK, Assistant Examiner US. Cl. X.R. 2602 

